De Niro, Keaton, Heigl and Seyfried also star in indie pic

Robert De Niro, Diane Keaton, Katherine Heigl, Amanda Seyfried and Topher Grace are set to star in the indie pic, which has also added Susan Sarandon, Ben Barnes and Patricia Rae to the ensemble.

Zackham (“The Bucket List”) is making his directorial debut with the film, which he also wrote.

De Niro and Keaton will play a long-divorced couple who, for the sake of their adopted son’s wedding and his very religious biological mother, pretend they’re still married. They quickly learn that acting the part isn’t easy, especially when their past, present and future unravel for all to see.

Barnes will play the groom opposite Seyfried’s bride, while Rae will play his Spanish-speaking birth mother who’s visiting America for the first time. As for Sarandon, she’ll play De Niro’s longtime girlfriend who caters the wedding to support the charade.

“Big Wedding” is a co-production between the helmer’s Two Ton Films banner and Millennium Films. Zackham and Two Ton’s Clay Pecorin will produce with Richard Salvatore and Harry Ufland, while Avi Lerner, Danny Dimbort and Trevor Short will exec produce. Production for the film is slated to start this July in Greenwich, Conn.

Williams was last seen in a trio of 2009 pics including “World’s Greatest Dad,” “Night at the Museum: Battle of the Smithsonian” and Disney’s “Old Dogs.” He’ll soon be heard in George Miller’s animated sequel “Happy Feet 2 in 3D,” which Warner Bros. will release on Nov. 18.